1. Field of the Invention
The present invention relates to an apparatus for controlling starting of an internal combustion engine and, more particularly, to an apparatus for controlling starting of an internal combustion engine so as to prevent a deterioration or reduce variation in exhaust emissions at the time of starting.
2. Description of the Related Art
Conventionally, an internal combustion engine is controlled as described below when started. When a driver turns on the ignition system to start an engine, energization of an engine control unit (hereinafter referred to as xe2x80x9cECUxe2x80x9d) for controlling the engine and various sensors and actuators attached to the engine is started. When the driver thereafter turns on the ignition switch, the starter is directly connected to the battery to crank the engine. When the engine cranks, the ECU controls the engine so that injection of fuel into the cylinders is started and ignition is effected in each cylinder.
In this conventional internal combustion engine starting control process, however, there is a possibility of the sensors and actuators attached to the engine being in conditions different from the optimum conditions if the starter is driven immediately after turning on the ignition system. For example, in a heating coil type of airflow sensor (AFS) provided as a means for measuring the intake air flow rate, the current supplied to the heating coil is controlled so that the temperature difference between air and the hearing coil is constant, and the supplied current is used as a passing air flow rate signal. The current supplied to heat up the heating coil is considerably large immediately after a start of AFS energization at engine startup, for example. In such a situation, the measured flow rate value is larger than the value corresponding to the actual intake air flow rate and there is a possibility of the air/fuel ratio being controlled so that the fuel-air rate is excessively rich and the amount of unburned HC is increased.
The period of time from the moment at which the ignition switch is turned on to the moment at which cranking is started depends on the driver. Because of this fact and the above-described drawback, exhaust emissions can vary considerably when the engine is started.
Ordinarily, the idle speed control (ISC) valve is in a fully opened position before the engine is started. When, after a start of the engine operation, the condition that the engine speed is equal to or higher than a fixed value while the battery voltage is equal to or higher than a fixed level is satisfied, a drive signal is supplied to a stepping motor for adjusting the opening amount of the ISC valve to start control of the intake air flow rate. Therefore, an amount of air larger than the necessary amount is required in at the time of starting and there is a possibility of an excessively large amount of fuel being injected to increase the amount of unburned HC.
Since the emission control has recently been made stricter as in the United States, it is necessary to reduce variations in exhaust emissions as well as to reduce exhaust emissions at the time of starting.
Moreover, the conventional internal combustion engine starting control also has a problem that, in the case of starting at an extremely low temperature, combustion is unstable even after the engine speed has become higher than the speed at which a starting mode is to be determined and there is a possibility of occurrence of an engine stall in such a case.
In view of the above-described problems of the conventional art, an object of the present invention is to provide an internal combustion engine starting control which stabilizes the output of the airflow meter mainly at startup and optimizes the startup opening amount of the ISC valve and, and which thereby reduces exhaust emissions and emission variations.
To achieve this object, according to the present invention, there is provided an apparatus for controlling starting of an internal combustion engine, comprising a starter for cranking the engine, engine starting command means for outputting an engine starting command for starting the engine, and starter control means for controlling drive of the starter on the basis of the engine starting command.
The starter control means drives the starter after a lapse of a predetermined period of time from the moment at which the engine starting command is input.
The apparatus may be further provided with engine water temperature detection means for detecting the temperature of engine cooling water. The starter control means changes the predetermined period of time according to the temperature of engine cooling water.
At least one sensor is provided in the engine, and the starter control means changes the predetermined period of time on the basis of the time necessary for the output from the sensor to stabilize.
An actuator is provided in the engine, and the starter control means changes the predetermined period of time on the basis of the time required to complete control of the actuator.
The apparatus may be further provided with engine revolution detection means for detecting the number of engine revolutions. The starter is stopped after a lapse of a predetermined period of time from the moment at which the number of engine revolutions becomes equal to or larger than a predetermined number of revolutions.